Technical Abstract:
Pasteurella haemolytica (PH) colonization of the upper respiratory tract (URT) was inhibited in experimentally vaccinated cattle. The objective was to identify iron-regulated immunogens related to protection. Serum and nasal secretions were analyzed by Western blots against outer membrane protein (OMP) preparation of PH which was grown in BHI broth with 150 mM 2,2"-dipyridyl and supplemented with 20 mg of bovine holotransferrin/ml. Vaccination elicited serum IgG antibody to iron-regulated OMPs. Serums were collected from vaccinated and nonvaccinated experimentally challenged cattle, and from nonvaccinated transported cattle involved in a field trial. The colonization status of the URT of each animal was determined. Nasal secretions were collected only from the experimentally challenged cattle. Most vaccinated cattle were not colonized, whereas most nonvaccinated cattle were colonized. Iron-regulated OMP were represented by yantigens of approximately 102, 80, 72, and 67 kDa. Vaccination elicited serum IgG antibody to the iron-regulated OMPs. Significantly more vaccinated, noncolonized cattle had serum IgG to the 80, 72, and 67 kDa antigens than vaccinated, colonized cattle. Most nonvaccinated cattle did not have antibody t the antigens. Nasal secretions from vaccinated and nonvaccinated cattle had IgA antibody to the 103, 80, and 72 kDa antigens. The data suggests that there is a positive relationship between serum IgG antibodies to iron-regulated OMPs and inhibition of colonization of the URT by P. Haemolytica.